The present invention generally relates to methods for sealing containers and, more specifically, to methods of sealing containers in a siftproof manner designed to prevent leakage of particulate contents or infestation by insects.
Many containers, such as cartons, boxes or other less rigid containers, are constructed from paper-based materials and include open ends each having a plurality of flaps. Typically, the flaps at each end include a pair of opposed major flaps and a pair of opposed minor flaps. The containers are usually folded from a flat condition into an erected condition, after which a desired product may be introduced into the container. The flaps are then folded and connected together, typically using an adhesive, to close the opposite ends of the container. The minor flaps are folded down first and the major flaps are folded down next and sealed to upper surfaces of the minor flaps using adhesive.
Particulate products, such as granulated or powdered products, require packaging that prevents leakage of the product during shipment and storage. Plastic liners may be used inside the container for this purpose, however, such liners increase packaging costs. To reduce costs, linerless siftproof containers and sealing methods have been developed for storing and shipping particulate products. The end flaps of these siftproof containers must be tightly sealed in a manner that prevents the contents from sifting out between the flaps and which likewise prevents infestation by insects through gaps between the flaps. In the past, all of the flaps have received adhesive deposits in the form of intermittent or continuous adhesive beads to ensure that the seams between the various flaps are sealed in a siftproof manner.
As the development of siftproof containers has progressed, certain problems have been addressed relative to siftproof seal integrity and costs associated with the adhesive and the paper construction products. For example, embossments have been used on the various flaps to provide opposed surfaces lying in close relation such that the gap between the flaps does not need to be filled with as much adhesive. Other siftproof containers have been configured to include a modified first major flap that enables direct contact between embossed portions of the minor flaps and a corresponding embossed portion of the second major flap. While these improvements have helped in some regards, modifying containers in these manners can also add expense and some containers cannot have embossed or otherwise modified flaps.
Other problems in this art relate to the need for a large of number of adhesive dispensers, or adhesive dispensing nozzles, necessary to place the corresponding number of beads on the container flaps extending in the conveying path of the containers. The increased complexity of the dispensing system increases costs and complicates changeover procedures. In this latter regard, for containers of different configurations and/or sizes, dispensing guns must be removed or added, or nozzles must be removed and plugged or added to accommodate the new configuration or container size.
Despite the various developments in the area of siftproof containers, improvements are still needed to maintain siftproof seal integrity while reducing adhesive requirements and general manufacturing costs. In this regard, the use of continuous adhesive sealing beads as opposed to a number of intermittent short and long beads only extending parallel to the conveying path requires much less adhesive and lower manufacturing equipment and changeover costs due to the lower number of necessary adhesive guns. However, applying a continuous adhesive bead in a direction generally perpendicular to the conveying path during high speed packaging operations has been a troublesome problem. Many packaging lines are designed to move at a rate of approximately 400-500 ft./min. or above and, at these high speeds, applying accurate beads of adhesive perpendicular to the direction of the conveying path has been a problem inadequately addressed by prior siftproof packaging systems. With the prior art high speed siftproof packaging methods, beads of adhesive have been applied only in the direction of the conveying path in order to deal with this problem. This results in the use of much more adhesive than necessary to create a siftproof pattern and necessitates the use of multiple side-by-side adhesive dispensing guns and/or nozzles mounted adjacent the conveying path.
To solve these and other problems in the art, it would be desirable to provide a method of applying a siftproof pattern of adhesive to the major and minor flaps of a container while using less adhesive and a lower number of adhesive dispensing components while still maintaining a high production rate in a high speed packaging operation.
The present invention provides a method of applying adhesive to respective first and second major flaps and first and second minor flaps of a container in a siftproof pattern. The container is moved along a conveying path with the major flaps being folded in an outwardly extending position and the minor flaps being folded in an inwardly extending position. With the container moving along the conveying path, a first gun is moved relative to the container while dispensing a first bead of adhesive therefrom along respective first edges of the first major flap and the first minor flap while moving the first dispensing gun in a direction generally perpendicular to the conveying path. The first bead may be applied starting on the first minor flap and moving onto the first major flap or vice versa. A second gun is moved relative to the container while dispensing a second bead of adhesive therefrom starting along the first edge of the first minor flap and continuing along a first edge of the second major flap in a direction generally perpendicular to the conveying path. With the first bead of adhesive completed and the first gun shut off, the second bead of adhesive is continued with the second gun held stationary. During this time, the container continues to move along the conveying path. The second bead of adhesive is continued along a second edge of second major flap in a direction generally parallel to the conveying path. The second bead of adhesive is then continued along a third edge of the second major flap and extending onto the second minor flap while moving the second dispensing gun again in a direction generally perpendicular to the conveying path. Preferably simultaneously with the dispensing of the second bead of adhesive along the third edge of the second major flap, a third bead of adhesive is dispensed from the first dispensing gun and extends along an edge of the first major flap and onto the second minor flap in a direction generally perpendicular to the conveying path and generally parallel to the first bead of adhesive. Like the first bead of adhesive, this third bead of adhesive may be started on the first major flap and extend onto the second minor flap or vice versa. The major flaps are then folded and sealed to the minor flaps by folding the first major flap onto the minor flaps and then folding the second major flap onto the first major flap.
In the preferred embodiment of the invention, only first and second adhesive dispensing guns are necessary in a high speed packaging operation to apply beads of adhesive in a siftproof pattern using minimal adhesive. Quick movements perpendicular to the direction of the conveying path will result in the necessary generally perpendicular beads of adhesive at opposite ends of the major and minor flaps. In the preferred embodiment, electric gun movers, such as linear actuators or servomotors with rotatable outputs, are used to facilitate this quick perpendicular movement. Even with the speed of the container along the conveying path reaching 400-500 ft./min. or above, the adhesive beads necessary in the direction generally perpendicular to the conveying path may be made, while the longer sealing bead extending in the direction of the conveying path is easily placed with the corresponding gun held in a stationary position.
In the preferred embodiment, the first and second guns are mounted along a linear guide rod and are initially moved in opposite directions perpendicular to the conveying path to apply respective beads of adhesive extending from the first minor flap onto the respective first and second major flaps. The first gun is then shut off or closed and the second gun is maintained on or opened to dispense a portion of the second bead along an edge which extends parallel to the conveying path. When the end of this portion of the bead is reached, the first dispensing gun is actuated to again dispense a bead of adhesive and each of the dispensing guns is moved toward the other in a direction generally perpendicular to the conveying path to again dispense beads of adhesive that extend from the first and second major flaps onto the second minor flap. This completes the siftproof pattern for the container and this method is repeated for each container continuously moving along the conveying path.
In an alternative embodiment, electrically-actuated servomotors with rotatable outputs are used to move the first and second guns in a generally perpendicular direction to the conveying path for the purposes discussed above. The manner of placing the adhesive beads is otherwise the same as discussed above with respect to the preferred embodiment. This alternative embodiment may also have manual adjustment mechanisms for accommodating containers and/or container flaps of different configurations and sizes. In each embodiment, the accommodation of containers and/or flaps of different sizes and configurations also may be made by suitable adjustment in an electrical control controlling the extent of movement for one or both dispensing guns.
These and other objects, advantages, and features of the invention will become more readily apparent to those of ordinary skill in the art upon review of the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings.